Effects of temperature and grain refinement on the closed-die forging of a micro gear

Abstract

Temperature and grain size are important factors for material flow behaviour and die filling in metal-forming processes. Their impacts are even greater in micro metal forming when the process is scaled from conventional down to micro dimensions because so-called size effects cause inhomogeneous material characteristics, leading to inaccuracy of shape and scatter of product properties. This study investigates the effects of temperature and grain refinement on the closed-die forging of a micro copper gear with a module of 0.4 mm, 12 teeth, and an integral shaft. A micro forging system equipped with heating devices was developed for conducting the experiments at elevated temperature. Moreover, equal-channel angular extrusion and heat treatments were applied to control the mean grain size of the copper in a range between 4 and 46 μm. The experimental results show that the increase of forming temperature and the grain refinement can improve material flow behaviour, resulting in better filling of tooth cavities, more uniform hardness distributions, and smoother tooth profiles.